Metal-organic framework composite with nano metal-organic frameworks embedded in host metal-organic framework, method for producing the metal-organic framework composite and gas storage including the metal-organic framework composite

ABSTRACT

Disclosed is a metal-organic framework composite including a host metal-organic framework, and nano metal-organic frameworks embedded In the host metal-organic framework. The host metal-organic framework and the nana metal-organic frameworks include different metals and organic ligands. The metal-organic framework composite has a structure in which the nano metal-organic frameworks are embedded in the host metal-organic framework. Due to this structure, defects are formed at the interfaces between the host metal-organic framework and the nano metal-organic frameworks, enabling the application of the metal-organic framework composite to gas storages with greatly improved gas storage efficiency. The metal-organic framework composite can be used as a gas adsorbent with very high efficiency due to its very large specific surface area. In addition, the metal-organic framework composite has high storage capacities for hydrogen, carbon dioxide, and methane and is thus very attractive from the viewpoint of industrial application. The metals and the ligands can be combined to make the metal-organic framework composite highly resistant to pressure, temperature, and water. Therefore, the metal-organic framework composite can also be applied to filters that can directly capture carbon dioxide from factory chimneys or can adsorb pollutants in water. Also disclosed are a method for producing the metal-organic framework composite and a gas storage using the metal-organic framework composite.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Korean PatentApplication No. 10-2015-0130343 filed on Sep. 15, 2015 in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference is its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a metal-organic framework compositeincluding a host metal-organic framework and nano metal-organicframeworks embedded in the host metal-organic framework, a method forproducing the metal-organic framework composite, and a gas storage usingthe metal-organic framework composite. More particularly, the presentinvention relates to the use of a host metal-organic framework and nanometal-organic frameworks including different metals and organic ligands,the production of a metal-organic framework composite in which the nanometal-organic frameworks are embedded in the host metal-organicframework, and the application of the metal-organic framework compositeto a gas storage.

2. Description of the Related Art

Metal-organic frameworks were first reported by Omar M. Yaghi, aprofessor of the University of California, Berkeley (USA) (Non-patentDocument 1). Metal-organic frameworks are synthesized from metalprecursors and organic ligands as linkers in a particular solvent by ahydrothermal method and have a three-dimensional porous structure inwhich the metal blocks and the organic ligands are repeatedly arranged.Metal-organic frameworks have a very large specific surface area due tothe presence of micropores or mesopores. Metal-organic frameworks havereceived attention as materials for gas storage disc to their largespecific surface area. Another advantage of metal-organic frameworks isthat metal precursors can be very freely combined with organic ligands.Due to these advantages, thousands of metal-organic frameworks have beenregistered in the database so far.

Metal-organic frameworks were synthesized using a single metal and asingle organic ligand in the early days (Patent Document 1). Since then,methods have been reported for the synthesis of various organic ligandsto adjust the pore size of metal-organic frameworks. There have alsobeen a number of reports on methods for the synthesis of metal-organicframeworks suitable for the manufacture of more effective gas storagesby mixing many metals with different organic ligands.

Furthermore, a metal-organic framework having a functionalized organicligand capable of promoting a catalytic reaction was synthesized(Non-patent Document 2). The functionalization of the organic ligand canmaximize the catalytic reaction because pores of the metal-organicframework are used as active sites.

Methods tor synthesizing core/shell structured metal-organic frame-workswere proposed (Non-patent Document 3). The core and shell parts are madeof the same metal and the organic ligands have the same size in order tomaintain the lattices of metal-organic frameworks. Such syntheticmethods are designed such that metal-organic frameworks can moreefficiently store gases, such as hydrogen, carbon dioxide, and methane,further improvements are still needed.

Initial research on the synthesis of metal-organic frameworks has beendirected to increasing the efficiency of metal-organic frameworks basedon the use of new metals and organic ligands and further research hasbeen conducted on the mechanism of gas storage for higher efficiency,leading to a better understanding of the mechanism of gas storage. Basedon this research, the synthesis of structures in which micropores andmesopores coexist was reported (Non-patent Document 4). The coexistenceof micropores and mesopores allows gas molecules to easily enter throughthe mesopore regions, enabling gas storage. However, the smallermicropores block the escape of the gas molecules in the larger mesopores(“self-sequestering”).

Metal-organic frameworks have very high capacities for gas storage.However, physisorption to pores having a large specific surface arealimits practical applications of metal-organic frameworks to gasstorages. To overcome this limitation, there is a need for a newsynthetic method for metal-organic frameworks and a new gas storagemechanism.

The present inventors have found that when a host metal-organicframework and nano metal-organic frameworks including different metalsand organic ligands are used, a metal-organic framework composite can beproduced in which the nano metal-organic frameworks are embedded in thehost metal-organic framework. The present inventors have also found thatthe metal-organic framework composite can be applied to gas storageswith greatly improved gas storage efficiency. The present invention hasbeen accomplished based on these findings.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Korean Patent No. 10-0967631

Non-patent Documents

Non-patent Document 1: Yaghi, O. M. et al., J. Am. Chew. Soc., 136,5666-5667 (2004)

Non-patent Document 2: P. Dau et al., chem commun., 48, 9370-9372 (2012)

Non-patent Document 3: K. Koh et al., chem common., 41, 6162-6164 (2009)

Non-patent Document 4: Jung H, Park et al., Sci. Rep. 5, 12045 (2015)

SUMMARY OF THE INTENTION

The present invention has been made in view of the above problems, andit is an object of the present invention to provide a metal-organicframework composite in which nano metal-organic frameworks are embeddedin a host metal-organic framework including a metal and a liganddifferent from those included in the nano metal-organic frameworks, anda method for producing the metal-organic framework composite.

An aspect of the present invention provides a metal-organic frameworkcomposite including a host metal-organic framework and nanometal-organic frameworks embedded in the host metal-organic framework,the host metal-organic framework, and the nano metal-organic frameworksbeing represented by Formulae 1 and 2, respectively:

M1_(x1)O_(z1)(L1G1)_(y1)   (1)

M2_(x2)O_(z2)(L1G2)_(y2)   (2)

wherein M1 and M2 are different from each other and are eachindependently selected from copper (Cu), iron (Fe), chromium (Cr), zinc(Zn), aluminum (Al), magnesium (Mg), nickel (Ni), europium (Eu),gadolinium (Gd), and terbium (Tb), L1G1 and L1G2 are different from eachother and are each independently selected from 1,4-benzenedicarboxylate(BDC), 1,3,5-benzenetricarboxylate (BTC),4,4′,4″-benzene-1,3,5-triyl-tribenzoate (BTB),4,4,4″-(benzene-1,3,5-triyl-tris(benzene-4,1-diyl))tribenzoate) (BBC),4,4′,4″-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tribenzoate (BTE),5,5′,5″-((((benzene-1,3,5-triyltris(benzene-4,1-diyl)tris(ethyne-2,1-diyl))-tris(benzene-4,1-diyl))tris(ethyne-2,1-diyl))triisophthalate(BHEHPI), 4,4′,4″-1,3,5-triazine-2,4,6-triyl)tribenzoate (TATB),5,5′,5″-((benzene-1,3,5-tricarbonyl)tris(azanediyl))triisophthalate(TPBTM), 4,4′,4″-(benzene-1,3,5-triyl)tris(pyrazol-1-ide) (BTP),5,5′,5″-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))triisophthaiate(BTEI),5,5′,5″-(benzene-1,3,5-triyl-tris(biphenyl-4,4′-diyl))triisophthalate(BTTI),5,5′,5″-(((benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tris(benzene-4,1-diyl))tris(ethyne-2,1-diyl))triisophthalate(TTEI),5′,5″″,5″″″′-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tris(([1,1′:3′,1″-tarphenyl]-4,4″-dicarboxylate))(BTETCA),5,5′,5″-(((benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tris(benzene-4,1-diyl-tris(buta-1,3-diyne-4,1-diyl))triisophthalate(BNETPI),5,5′,5″-(benzene-1,3,5-triyl-tris(buta-1,3-diyl-4,1-diyl))triisophthalate(BHEI), dioxidoterephthalate (DOT), adamantane-1,3,5,7-tetracarboxylate(ATC), 6,6′-dichloro-4,4-di(pyridin-4-yl)-[1,1′-binaphthalene]-2,2′-diol(DCDPBN), imidazole dicarboxylate (ImDC),4,4′-([2,2′-bipyridine]-5,5′-diyl)dibennzoate (DPBPyDC),2-phenylpyridine (PPy), 2,4,6-trihydroxy-1,3,5-benzenetrisulfonate(THBTS), 3,3′,5,5′-azobenzenetetracarboxylate (ADB), and4,4′-(2,5,8,11,14,16,19,22,25,28-decaoxa-1,15(1,4)-dibenzacyclooctacosaphane-1²,1⁵-diylbis(ethyne-2,1-diyl))dibenzoate(BPP34C10DA), x1 is an integer from 1 to 6, x2 is an integer from 1 to6, z1 is an integer from 1 to 4, z2 is an integer from 1 to 4, y1 is aninteger from 1 to 6, and y2 is an integer from 1 to 6.

In Formulae 1 and 2, M1 is Zn, L1G1 is BDC, M2 is Cu, L1G2 is BTC, x1 is4, z1 is 1, y1 is 3, x2 is 3, z2 is 0, and y2 is 2.

The nano metal-organic frameworks have a size of 5 to 300 nm.

The nano metal-organic frameworks have a pore size of 5 to 7 Å and thehost metal-organic framework has a pore size of 8 to 10 Å.

The nano metal-organic frameworks have a BET specific surface area of1370 to 1570 m²/g and the metal-organic framework composite has a BETspecific surface area of 3300 to 3500 m²/g.

L1G1 and L1G2 are in a molar ratio of 9-10:1.

The present invention also provides a gas storage including themetal-organic framework composite.

The present invention also provides a methane storage including themetal-organic framework composite.

The present invention also provides a dye-captured metal-organicframework composite including (i) the metal-organic framework compositeand (ii) a dye captured in the nano metal-organic frameworks.

The present invention also provides a method for producing ametal-organic framework composite, including (b) subjecting a solutionincluding a second metal precursor, a second organic ligand, a secondorganic solvent, and nano metal-organic frameworks to a hydrothermalreaction wherein the metal-organic framework composite includes a hostmetal-organic framework and nano metal-organic frameworks embedded inthe host metal-organic framework, the second metal precursor is selectedfrom Co, Fe, Cr, Zn, Al, Mg, Ni, En, Gd, and Tb precursors, the secondorganic ligand is selected from BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB,TPBTM, BTP, BTEI, BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN,ImDC, DPBPyDC, PPy, THBTS, ADS, and BPP34C10DA, the second organicsolvent is selected from dimethylformamide, diethylformamide,N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylscelamide, methanol,ethanol, water, and mixtures thereof the host metal-organic frameworkand the nano metal-organic frameworks being represented by Formulae 1and 2, respectively:

M1_(x1)O_(z1)(L1G1)_(y1)   (1)

M2_(x2)O_(x2)(L1G2)_(y2)   (2)

wherein M1 and M2 are different from each other and are eachindependently selected from Cu, Fe, Cr, Zn, Al, Mg, Ni, Eu, Gd, and Tb,L1G1 and L1G2 are different from each other and are each independentlyselected from BDC, BTC, BTB, BBC, BTE, BBEHPI, TATB, TPBTM, BIT, BTEI,BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN, ImDC, DPBPyDC, PPy,THBTS, ADB, and BPP34C10DA, x1 is an integer from 1 to 6, x2 is aninteger from 1 to 6, z1 is an integer from 1 to 4, z2 is an integer from1 to 4, y1 is an integer from 1 to 6, and y2 is an integer from 1 to 6.

The method further includes (a) mixing a first metal precursor, a firstorganic ligand, and a first organic solvent and reacting the mixturewith stirring at room temperature to prepare the nano metal-organicframeworks wherein the first metal precursor is selected from Cu, Fe,Cr, Zn, Al, Mg, Ni, Eu, Gd, and Tb, the first organic ligand is selectedfrom BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB, TPBTM, BTP, BTEI, BTTI,TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN, ImDC, DPBPyDC, PPy, THBTS,ADB, and BPP34C10DA, and the first organic, solvent is selected fromdimethylformamide, diethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, dimethylacetamide, methanol, ethanol, water, and mixturesthereof.

The method further includes activating the nano metal-organic frameworksand the host metal-organic framework in ethanol or chloroform as asolvent for 30 to 40 hours, followed by drying under vacuum at 100 to120° C.

The first, metal precursor is a Cu precursor, the first organic ligandis BTC, the second metal precursor is a Zn precursor, the second organicligand is BDC, the first organic solvent is a mixture ofdimethylformamide, methanol, and water in a volume ratio of0.7-1:0.7-1:0.7-1, and the second organic solvent is diethylformamide.

The Cu precursor and the BTC are in a weight ratio of 2.0-2.3:1.1-1.5.

The Zn precursor and the BDC are in a weight ratio of 17-18:3.5-4.0.

The hydrothermal reaction is carried out at 110 to 130° C. for 7 to 9hours.

The present invention also provides a method for producing adye-captured metal-organic framework composite, including (A) allowing adye to be captured in nano metal-organic frameworks and (B) subjecting asolution of the dye-captured nano metal-organic frameworks, a secondmetal precursor, a second organic ligand, and a second organic solventto a hydrothermal reaction wherein the second metal precursor isselected from Cu, Fe, Cr, Zn, Al, Mg, Mi, Eu, Gd, and Tb, the secondorganic ligand is selected from BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB,TPBTM, BTP, BTEI, BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN,ImDC DPBPyDC, PPy, THBTS, ADB, and BPP34C10DA, and the second organicsolvent is selected torn dimethylformamide, diethylformamide,N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, methanol,ethanol, water, and mixtures thereof.

As described above, the metal-organic framework composite of the presentinvention can be produced using a host metal-organic framework and nanometal-organic frameworks including different metals and organic ligands.The metal-organic framework composite has a structure in which the nanometal-organic frameworks are embedded in the host metal-organicframework. Due to this structure, defects are formed at the interfacesbetween the host metal-organic framework, and the nano metal-organicframeworks, enabling the application of the metal-organic frameworkcomposite to gas storages with greatly improved gas storage efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1a is a diagram showing a procedure for producing a metal-organicframework composite through Preparative Examples 1 and 2;

FIG. 1b shows the structure of a metal-organic framework compositesynthesized in Example 1;

FIG. 2a shows a graph showing the X-ray diffraction (XRD)characteristics of nano metal-organic frameworks prepared In PreparativeExample 1;

FIG. 2b is a graph showing the BET specific surface area (N₂ isothermal)of the nano metal-organic frameworks;

FIG. 2c shows a scanning electron microscopy (SEM) image of the nanometal-organic, frameworks;

FIG. 2d shows a size distribution profile of the nano metal-organicframeworks, which was measured using dynamic light scattering (DLS);

FIG. 3a is a graph showing the X-ray diffraction (XRD) characteristicsof nano metal-organic frameworks prepared in Preparative Example 1, ahost metal-organic framework prepared in Preparative Example 2, and ametal-organic framework composite synthesized in Example 1;

FIG. 3b is a graph showing the BET specific surface area (N₂ Isothermal)of the nano metal-organic frameworks, the host metal-organic frameworkand the metal-organic framework composite;

FIG. 3c shows a nuclear magnetic resonance (NMR) spectrum of themetal-organic framework composite;

FIG. 4 shows a pore size distribution profile of a metal-organicframework composite synthesized in Example 1;

FIG. 5 shows a thermogravimetric analysis (TGA) curve of a metal-organicframework composite synthesized in Example 1;

FIG. 6a shows an optical microscopy image of a metal-organic frameworkcomposite synthesized in Example 1, which was measured in bright/darkfield mode;

FIG. 6b shows a scanning transmission electron microscopy (STEM) imageof the metal-organic framework composite;

FIG. 6c shows a higher magnification high-angle annular dark fieldscanning transmission electron microscopy (HAADF STEM) image of 2 b;

FIG. 6d shows mapping images of the metal-organic framework composite;

FIG. 7 shows scanning electron microscopy (SEM) images of the crystalsurfaces and crystal interiors of a host metal-organic frameworkprepared in Preparative Example 2 and a metal-organic frameworksynthesized in Example 1;

FIG. 8a shows a high-resolution transmission electron microscopy (HRTEM)image of a randomly selected point of a metal-organic frameworkcomposite synthesized in Example 1;

FIG. 8b shows a higher magnification image of FIG. 8a

FIG. 8c shows a another high-resolution transmission electron microscopy(HRTEM) image of a randomly selected point of a metal-organic frameworkcomposite synthesized in Example 1;

FIG. 8d shows a high-angle annular dark field scanning transmissionelectron microscopy (HAADF STEM) image of FIG. 8 c;

FIG. 9a shows a confocal microscopy image of a host metal-organicframework prepared in Preparative Example 2;

FIG. 9b shows a confocal microscopy image of a state in which Rhodaminedye was embedded in the pores of nano metal-organic frameworks preparedin Preparative Example 1;

FIG. 9c shows a confocal microscopy image of a structure in which theRhodamine dye-embedded nano metal-organic frameworks were embedded inthe host metal-organic framework;

FIG. 10a shows a graph comparing the methane (CH₄) uptake capacities ofnano metal-organic frameworks prepared in Preparative Example 1, a hostmetal-organic framework prepared in Preparative Example 2, and ametal-organic framework composite synthesized in Example 1;

FIG. 10b shows a graph comparing the characteristics of themetal-organic framework composite grown in different vials (baths);

FIG. 10c is a graph showing the cycle characteristics of themetal-organic framework composite; and

FIG. 11 shows a graph comparing the methane (CH₄) uptake capacities of ahost metal-organic framework (MOF-5) prepared in Preparative Example 2,a metal-organic framework composite (nHKUST-1(4 ml)⊂MOF-5) synthesizedin Example 1, and a metal-organic framework composite_2 (nHKUST-1(2ml)⊂MOF-5) synthesized in Example 2.

DETAILED DESCRIPTION OF THE INVENTION

Several aspects and various embodiments of the present invention willnow be described in more detail.

The present invention provides a metal-organic framework compositeincluding a host metal-organic framework and nano metal-organicframeworks embedded in the host metal-organic framework, the hostmetal-organic framework and the nano metal-organic frameworks beingrepresented by Formulae 1 and 2, respectively:

M1_(x1)O_(z1)(L1G1)   (1)

M2_(x2)O_(z2)(L1G2)_(y2)   (2)

wherein M1 and M2 are different from each other and are eachindependently selected from Cu, Fe, Cr, Zn, Al, Mg, Ni, Eu, Gd, and Tb,L1G1 and L1G2 are different from each other and are each independentlyselected from BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB, TPBTM, BTP, BTEI,BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN, ImDC, DPBPyDC, PPy,THBTS, ADB, and BPP34C10DA, x1 is an integer from 1 to 6, x2 is anInteger from 1 to 6, z1 is an integer from 1 to 4, z2 is an integer from1 to 4, y1 is an integer from 1 to 6, and y2 is m1 integer from 1 to 6.In the metal-organic framework composite of the present invention, thehost metal-organic framework and the nano metal-organic frameworksInclude different metals and organic ligands. The metal-organicframework composite of the present invention has excellent gas storageproperties compared to the single use of the host metal-organicframework or the nano metal-organic frameworks.

In Formulae 1 and 2, M1 is Zn, L1G1 is BDC, M2 is Cu, L1G2 is BTC, x1 is4, z1 is 1, y1 is 3, x2 is 3, z2 is 0, and y2 is 2. Particularly, themetal-organic framework composite has a high methane storage capacity of197 mg/g, which corresponds to 250% of the volumetric capacity of astorage material commonly used in a compressed natural gas (CNG) tank atroom temperature and 80 bar, when the host metal-organic framework isbased on zinc and the nano metal-organic frameworks embedded in the hostmetal-organic framework is based on copper. This demonstrates superiorgas storage capacity of the metal-organic framework composite accordingto the present invention, taking into consideration the fact thatmethane has a specific energy density as high as 15,400 Wh/kg.

The nano metal-organic frameworks have a size in the range of 5 to 300nm. Outside this range, it is difficult for the nano metal-organicframeworks to form interfacial defects with the host metal-organicframework, which is disadvantageous in gas storage. Preferably, the nanometal-organic frameworks have a size of 5 to 100 nm.

The nano metal-organic frameworks have a pore size of 5 to 7 Å and thehost metal-organic framework has a pore size of 8 to 10 Å. The nanometal-organic frameworks have a BET specific surface area similar tothat of the host metal-organic framework, interestingly, the nanometal-organic frameworks and fee host metal-organic framework wereconfirmed to have different pore size distributions. The use of themetal-organic frameworks having different pore sizes for the productionof the metal-organic framework composite facilitates the formation ofdefects at the interfaces between the host metal-organic framework andthe nano metal-organic frameworks, leading to an improvement in gasstorage capacity.

The nano metal-organic frameworks have a BET specific surface area, of1370 to 1570 m²/g and the metal-organic framework composite has a BETspecific surface area of 3300 to 3500 m²/g. A high BET specific surfacearea of the nano metal-organic frameworks is obtained when the pores arecompletely empty by activation during preparation. Considering thestructure of the metal-organic framework composite in which the nanometal-organic frameworks are embedded In the host metal-organicframework, the metal-organic framework composite has a BET specificsurface area similar to that of the host metal-organic framework.

L1G1 and L1G2 are in a molar ratio of 9-10:1. It is particularlypreferred that the molar ratio of the organic ligand of the hostmetal-organic framework to the organic ligand of the nano metal-organicframeworks is 9.0-9.5:1. The molar ratio of the organic ligandscontributes to a reduction in the pore size of the metal-organicframework composite, leading to an increase in specific surface area. Asa result an increased amount of gas is adsorbed to the metal-organicframe work.

The present invention also provides a gas storage including themetal-organic framework composite. The metal-organic framework compositeof the present invention has defects at the interfaces between the nanometal-organic frameworks and the host, metal-organic framework and alarge specific surface area, achieving high gas storage capacity.Therefore, the metal-organic framework composite is very effective forgas storage when applied to a hydrogen, carbon dioxide or methanestorage.

The present Invention also provides a methane storage including themetal-organic framework composite. Particularly, the high methane (CH₄)uptake capacity of the metal-organic framework composite makes themethane storage very effective to store methane.

The present invention also provides a dye-captured metal-organicframework composite including (i) the metal-organic framework compositeand (ii) a dye captured in the nano metal-organic frameworks. The nanometal-organic frameworks have the ability to encapsulate guestmolecules, such as dye molecules. After encapsulation, the guestmolecules can be embedded in the host metal-organic framework.

The present invention also provides a method for producing ametal-organic framework composite, including (b) subjecting a solutionincluding a second metal precursor, a second organic ligand, a secondorganic solvent, and nano metal-organic frameworks to a hydrothermalreaction wherein the metal-organic framework composite includes a hostmetal-organic framework and nano metal-organic frameworks embedded inthe host metal-organic framework, the second metal precursor is selectedfrom Cu, Fe, Cr, Zn, Al, Mg, M, Eu, Gd, and Tb, the second organicligand is selected from BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB, TPBTM,BTP, BTEI, BTTI, TTEI, BTETCA, BNETPI, BBEI, DOT, ATC, DCDPBN, ImDC,DPBPyDC, PPy, THBTS, ADB, and BPP34C10DA, the second organic solvent isselected from dimethylformamide, diethylformamide,M-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, methanol,ethanol, water, and mixtures thereof, the host metal-organic frameworkand the nano metal-organic frameworks being represented by Formulae 1and 2, respectively:

M1_(x1)O_(z1)(L1G1)_(y1)   (1)

M2_(x2)O_(x2)(L1G2)_(y2)   (2)

wherein M1 and M2 are different from each other and are eachindependently-selected from Cu, Fe, Cr, Zn, Al, Mg, M, Eu, Gd, and Tb,L1G1 and L1G2 are different from each other and are each independentlyselected from BDC, BTC, BIB, BBC, BTE, BHEHPI, TATB, TPBTM, BTP, BTEI,BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN, ImDC, DPBPyDC, PPy,THBTS, ADB, and BPP34C10DA, x1 is an integer from 1 to 6, x2 is aninteger from 1 to 6, z1 is an integer from 1 to 4, z2 is an integer from1 to 4, y1 is an integer from 1 to 6, and y2 is an integer from 1 to 6.Conventional synthetic methods for embedding nanomaterials inmetal-organic frameworks involve complicated processes, such asprocesses associated with the use of surfactants. In contrast, themethod of the present invention involves very simple solvation, enablingefficient synthesis of a metal-organic framework composite.

The method further includes (a) mixing a first metal precursor, a firstorganic-ligand, and a first organic solvent and reacting the mixturewith stirring at room, temperature to prepare the nano metal-organicframeworks wherein the first metal precursor is selected from Cu, Fe,Cr, Zn, Al, Mg, M, En, Gd, and Tb, the first organic ligand is selectedfrom BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB, TPBTM, BTP, BTEI, BTTI,TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN, ImDC, DPBPyDC, PPy, THBTS,ADB, and BPP34C10DA, and the first organic solvent is selected fromdimethylformamide, diethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, dimethylacetamide, methanol, ethanol, water, and mixturesthereof. Unlike previously reported methods for synthesizingmetal-organic frameworks, the method, of the present invention includesembedding nano metal-organic frameworks in a host metal-organicframework so that crystal lattice mismatch can occur at the interfacesbetween the nano metal-organic frameworks and the bulky host,metal-organic framework, leading to an improvement in gas storageproperties.

The method further includes activating the nano metal-organic frameworksand the host metal-organic framework in ethanol or chloroform as asolvent for 30 to 40 hours, followed by drying under vacuum at 100 to120° C. Particularly, the activation is performed to dissolve and removeresidues in the pores of the metal-organic frameworks using the solvent.The empty spaces of the pores are filled with the solvent. The drying isperformed to remove the solvent from the pores, leaving the porescompletely empty.

The first metal precursor is a Cu precursor, the first organic ligand isBTC, the second metal precursor is a Zn precursor, the second organicligand is BDC, the first organic solvent is a mixture ofdimethylformamide, methanol and water in a volume ratio of0.7-1:0.7-1:0.7-1, and the second organic solvent is diethylformamide.The use of the first organic solvent and the second organic solvent ismore particularly preferred because high porosity of the metal-organicframework composite is obtained.

The Cu precursor and the BTC are in a weight ratio of 2.0-2.3:1.1-1.5and the Zn precursor and the BDC are in a weight ratio of 17-18:3.5-4.0.When the weight ratios between the metal precursors and the organicligands are within the respective ranges defined above, excellent cyclecharacteristics of the metal-organic frame work, composite can beensured.

The hydrothermal reaction is carried out at 110 to 130° C. for 7 to 9hours. The hydrothermal reaction may not be sufficiently carried out ata temperature lower than 110° C. Meanwhile, a hydrothermal reactiontemperature higher than 130° C. may incur an increase in productioncost. If the hydrothermal reaction time is shorter than 7 hours, thecrystal phases of the metal-organic frameworks may not be well-defined.Meanwhile, if the hydrothermal reaction time is longer than 9 hours, theskeletal structures of the metal-organic frameworks may collapse.

The present invention also provides a method for producing adye-captured metal-organic framework composite, including (A) allowing adye to be captured in nano metal-organic frameworks and (B) subjecting asolution of the dye-captured nano metal-organic frameworks, a secondmetal precursor, a second organic ligand, and a second organic solventto a hydrothermal reaction wherein the second metal precursor isselected from Cu, Fe, Cr, Zn, AL Mg, Ni, Bu, Gd, and Tb, the secondorganic ligand is selected from BDC, BTC, BIB, BBC, BTB, BHEHPI, TATB,TPBTM, BTP, BTEI, BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN,ImDC, DPBPyDC, PPy, THBTS, ADB, and BPP34C10DA, and the second organicsolvent is selected from dimethylformamide, diethylformamide,N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, methanol,ethanol, water, and mixtures thereof. According to the method of thepresent invention, nano metal-organic frameworks are allowed to capturedye molecules and the dye-captured nano metal-organic frameworks arethen embedded in a host metal-organic framework to produce adye-captured metal-organic framework composite, which can be applied todye capture/storage technology.

PREPARATIVE EXAMPLE 1 Preparation of Nano Metal-Organic Frameworks

Copper acetate monohydrate (215 mg) as a copper precursor and1,3,5-benzenetricarboxylic acid (125 mg) as an organic ligand weredissolved in a mixture solution of dimethylformamide (DMF), ethanol, anddistilled water (each 25 ml). The solution was allowed to react withstirring in a round bottom flask at room temperature to obtain a blueprecipitate. After completion of the reaction, the precipitate wascollected by centrifugation at 9000 rpm for 10 mm, washed withdimethylformamide and ethanol, immersed in ethanol for 3 days foractivation, and dried in a vacuum oven at 100° C. for 24 h, giving nanometal-organic frameworks (“nHKUST-1”).

PREPARATIVE EXAMPLE 2 Preparation of Solution of Host Metal-OrganicFramework

Zinc nitrate tetrahydrate (1764 mg) as a zinc precursor and1,4-benzenedicarboxylic acid (375 mg) as an organic ligand weredissolved in 16 ml of dimethylformamide to prepare a solution of a hostmetal-organic framework (“MOF-5”). The nano metal-organic frameworksprepared in Preparative Example 1 were embedded in the zinc-based hostmetal-organic framework in the subsequent process.

EXAMPLE 1 Synthesis of Metal-Organic Framework Composite

The host metal-organic framework, solution prepared in PreparativeExample 2 was placed in a 30 ml vial. The nano metal-organic frameworksprepared in Preparative Example 1 were dispersed in 20 ml ofdimethylformamide. 4 ml of the dispersion was added to the hostmetal-organic framework solution prepared in Preparative Example 2. Theresulting mixture solution was initially opaque blue but turnedtransparent blue after sonication for 20 min. The solution was subjectedto a hydrothermal reaction at 110° C. for 7 h. The obtained crystal waswashed with dimethylformamide, immersed in chloroform for 3 days foractivation, and dried in a vacuum oven at 120° C. for 24 h, giving ametal-organic framework composite (“nHKUST-1⊂MOF-5”).

EXAMPLE 2 Synthesis of Metal-Organic Framework Composite_2

A metal-organic framework composite (“nHKUST-1⊂MOF-5_2”) was synthesizedin the same manner as in Example 1, except that 2 ml of the dispersionwas added.

FIG. 1a is a diagram showing the procedure for producing themetal-organic framework composite through Preparative Examples 1 and 2and FIG. 1b shows the structure of the metal-organic framework compositesynthesized in Example 1. The mixture solution of the nano metal-organicframeworks prepared in Preparative Example 1 and the host metal-organicframework prepared in Preparative Example 2 was initially opaque by thesuspended particles of the nano metal-organic frameworks prepared inPreparative Example 1. (see FIG. 1b ). After the subsequent 20-minsonication, the mixture solution was changed to a transparent bluesolution free of fine particles. The hydrothermal reaction of thetransparent blue solution enabled the production of the metal-organicframework composite in which the nano metal-organic frameworks wereembedded in the host metal-organic framework (see FIG. 1b ).

FIG. 2a shows a graph showing the X-ray diffraction (XRD)characteristics of the nano metal-organic frameworks prepared inPreparative Example 1, FIG. 2b a graph showing the BET specific surfacearea (N₂ isothermal) of the nano metal-organic frameworks, FIG. 2c showsa scanning electron microscopy (SEM) image of the nano metal-organicframeworks, and FIG. 2d shows a size distribution profile of the nanometal-organic frameworks, which was measured using dynamic lightscattering (DLS). As can be seen from FIG. 2 a, a main peak of the nanometal-organic frameworks appeared at 2θ≦10°. The nano metal-organicframeworks were of Type 1 and had a specific surface area of about 1470m²/g, as determined by BET measurement using nitrogen (see FIG. 2b ).The SEM image reveals that the nano metal-organic framework particleshad a relatively uniform size of about 100 nm and were not separatedfrom each other (see FIG. 2c ). The size distribution profile of thenano metal-organic frameworks was measured using dynamic lightscattering (DLS). As a result, the nano metal-organic frameworks wereconfirmed to have a uniform size of about 100 nm (see FIG. 2d ).

FIG. 3a shows a graph showing the X-ray diffraction (XRD)characteristics of the nano metal-organic frameworks prepared InPreparative Example 1, the host metal-organic framework prepared inPreparative Example 2, and the metal-organic framework compositesynthesized in Example 1, FIG. 3b is a graph showing the BET specificsurface area (N₂ isothermal) of the nano metal-organic frameworks, thehost metal-organic framework, and the metal-organic framework composite,and FIG. 3c shows a nuclear magnetic resonance (NMR) spectrum, of themetal-organic framework composite. In FIG. 3 a, the XRD patterns of thenano metal-organic frameworks (nHKUST-1), the host metal-organicframework (MOF-5), the pristine metal-organic framework composite (nHKUST-1⊂MOF-5 (Pristine)), and the metal-organic framework composite in theform of a powder (nHKUST-1⊂MOF-5 (Ground)) are shown from the bottom.The diffraction peaks of the host metal-organic framework (MOF-5)appeared at the same 2θ angles as those of the pristine metal-organicframework composite (nHKUST-1⊂MOF-5 (Pristine)) and the metal-organicframework composite in the form of a powder (nHKUST-1⊂MOF-5 (Ground)).In contrast the diffraction peaks of the nano metal-organic frameworks(nHKUST-1) did not appear in the pristine metal-organic frameworkcomposite (nHKUST-1⊂MOF-5 (Pristine)) and were observed in themetal-organic framework composite in the form of a powder(nHKOST-1⊂CMOF-5 (Ground)). These results demonstrate that the nanometal-organic frameworks (nHKUST-1) were embedded In the hostmetal-organic framework (MOF-5) rather than supported on the hostmetal-organic framework (MOF-5).

From FIG. 3 b, it can be confirmed that the metal-organic frameworkcomposite in which the nano metal-organic structures were embedded inthe host metal-organic framework had a specific surface area of 3400m²/g, which was not significantly different from that of the hostmetal-organic framework in which the nano metal-organic structures werenot embedded.

From the NMR spectrum, the organic ligand of the nano metal-organicframeworks and the organic ligand of the host metal-organic frame workwere detected at 8.6 ppm and 8.01 ppm, respectively, demonstrating thattheir molar ratio was 1:9.3 (see FIG. 3c ). The molar ratio indicatesthat 11 wt % of the nano metal-organic frameworks were embedded in thehost metal-organic framework. The results of inductively coupled plasmaatomic emission spectroscopy (ICP-AES) for the metals of the nanometal-organic frameworks (Cu, 10 wt %) and the host metal-organicframework (Zn, 90 wt %) also reveal that 1.1 wt % of the nanometal-organic frameworks were embedded in the host metal-organicframework.

FIG. 4 is a pore size distribution profile of the metal-organicframework composite synthesized in Example 1. The BET specific surfacearea of the metal-organic framework composite was similar to that of thehost metal-organic framework (see FIG. 3b ), but the nano metal-organicframeworks and the host metal-organic framework, were confirmed to havepore sizes of 6 Å and 9 Å, respectively (see FIG. 4).

FIG. 5 is a themiogravimetric analysis (TGA) curve of the metal-organicframework composite synthesized in Example 1. The results of TGA showthat the metal organic-framework composite was thermally stable at 400°C. or less.

FIG. 6a shows an optical microscopy image of the metal-organic frameworkcomposite synthesized in Example 1, which was measured in bright/darkfield mode, FIG. 6b shows a scanning transmission electron microscopy(STEM) image of the metal-organic framework composite, FIG. 6c shows ahigher magnification high-angle annular dark field scanning transmissionelectron microscopy (HAADF STEM) image of FIG. 6 b, and FIG. 6d showsmapping images of the metal-organic framework composite. FIG. 6a showsthat the nano metal-organic frameworks were embedded in the hostmetal-organic framework and FIG. 6b shows that the embedded nanometal-organic frameworks appeared brighter than the host metal-organicframework. FIG. 6c shows the detection of zinc from the hostmetal-organic framework (8.2 and 10.8 keV) and copper from the nanometal-organic frameworks (6.4 and 8.9 keV). The results of mapping forthe metal-organic framework composite show that the domains were divideddepending on the kinds of metals (see FIG. 6 d. Particularly, theinterfaces between the embedded nano metal-organic frameworks and thehost metal-organic framework were well-defined (see FIG. 6c ). Theformation of defects at the interfaces leads to an improvement in thegas storage properties.

FIG. 7 shows scanning electron microscopy (SEM) images of the crystalsurfaces and crystal interiors of the host metal-organic frameworkprepared in Preparative Example 2 and the metal-organic frameworksynthesized in Example 1. The images of the interiors of themetal-organic framework composite show the presence of the nanometal-organic frameworks having a size of 100 nm. The surface imagesshow that the surfaces of the metal-organic framework composite and thehost metal-organic framework were smooth.

FIGS. 8a and 8c show high-resolution transmission electron microscopy(HRTEM) images of two randomly selected points of the metal-organicframework composite synthesized in Example 1, FIG. 8b shows a highermagnification image of FIG. 9 a, and FIG. 8d shows a high-angle annulardark field scanning transmission electron microscopy (HAADF STEM) imageof FIG. 8 c. In FIG. 8a and FIG. 8 c, the central dark portions are thenano metal-organic frameworks and the circumferential portions representthe host metal-organic framework. FIG. 8a and FIG. 8d show that, therewere no gaps between the host metal-organic framework and the nanometal-organic frameworks, which indicates that the host metal-organicframework was in direct contact with the nano metal-organic frameworksat their interfaces. It was confirmed that the formation of the specificinterfaces led to an improvement in gas adsorption performance.

FIG. 9a shows a confocal microscopy image of the host metal-organicframework prepared in Preparative Example 2, FIG. 9b shows a confocalmicroscopy image of a state in which Rhodamine dye was embedded in thepores of the nano metal-organic, frameworks prepared in PreparativeExample 1, and FIG. 9c shows a confocal microscopy image of a structurein which the Rhodamine dye-embedded nano metal-organic frameworks wereembedded in the host metal-organic framework. The host metal-organicframework was not photosensitized, as shown in FIG. 9 a, but theRhodamine dye was embedded in the host metal-organic framework, asconfirmed in FIGS. 9b and 9 c.

FIG. 10a shows a graph comparing the methane (CH₄) uptake capacities ofthe nano metal-organic frameworks prepared in Preparative Example 1, thehost metal-organic framework prepared in Preparative Example 2, and themetal-organic framework composite synthesized In Example 1, FIG. 10bshows a graph comparing the characteristics of the metal-organicframework composite grown in different vials (baths), and FIG. 10c showsa graph showing the cycle characteristics of the metal-organic frameworkcomposite. The methane uptake capacities shown in FIG. 10a were measuredusing a magnetic suspension balance (MSB, Rubotherm). The methane uptakecapacities of the metal-organic framework composite were found to behigher by 14% and 36% than those of the nano metal-organic frameworksand the host metal-organic framework, respectively (see FIG. 10a ). Ascan be seen from FIG. 10 b, the same methane uptake results (197 mg/g)were obtained in the metal-organic framework composite grown indifferent vials (baths), demonstrating their generality. The methanesorption cycle characteristics of the metal-organic framework compositewere measured at room temperature (see FIG. 10c ), confirming that themetal-organic framework composite had superior cycle performance, highreversible capacity, and good stability.

FIG. 11 is a graph comparing the methane (CH₄) uptake capacities of thehost metal-organic framework (MOF-5) prepared in Preparative Example 2,the metal-organic framework composite (nHKUST-1(4 ml)⊂MOF-5) synthesizedin Example 1, and the metal-organic framework composite_2 (nHKUST-1(2ml)⊂MOF-5) synthesized in Example 2. As can be seen from FIG. 11, themethane uptake capacity was improved with increasing amount of the nanometal-organic frameworks embedded in the host metal-organic framework.

What is claimed is:
 1. A metal-organic framework composite comprising ahost metal-organic framework and nano metal-organic frameworks embeddedin the host metal-organic framework, the host metal-organic frameworkand the nano metal-organic frameworks being represented by Formulae 1and 2, respectively:M1_(x1)O_(z1)(L1G1)_(y1)   (1)M2_(x2)O_(x2)(L1G2)_(y2)   (2) wherein M1 and M2 are different from eachother and are each independently selected from Cu, Fe, Cr, Zn, Al, Mg,Nis Eu, Gd, and Tb, L1G1 and L1G2 are different from each other and areeach independently selected from BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB,TPBTM, BTP, BTEI, BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN,ImDC, DPBPyDC, PPy, THBTS, ADB, and BPP34C10DA, x1 is an integer from 1to 6, x2 is an integer from 1 to 6, z1 is an integer from 1 to 4, z2 isan integer from 1 to 4, y1 is an integer from 1 to 6, and y2 is aninteger from 1 to
 6. 2. The metal-organic framework composite accordingto claim 1, wherein M1 is Zn, L1G1 is BDC, M2 is Cu, L1G2 is BTC, x1 is4, z is 1, y1 is 3, x2 is 3, z2 is 0, and y2 is
 2. 3. The metal-organicframework composite according to claim 1, wherein the nano metal-organicframeworks have a size of 5 to 300 nm.
 4. The metal-organic frameworkcomposite according to claim 1, wherein, the nano metal-organicframeworks have a pore size of 5 to 7 Å and the host metal-organicframework has a pore size of 8 to 10 Å.
 5. The metal-organic frameworkcomposite according to claim 1, wherein the nano metal-organicframeworks have a BET specific surface area of 1370 to 1570 m²/g and themetal-organic framework composite has a BET specific surface area of3300 to 3500 m²/g.
 6. The metal-organic framework composite according toclaim 1, wherein L1G1 and L1G2 are in a molar ratio of 9-10:1.
 7. A gasstorage comprising the metal-organic framework composite according toclaim
 1. 8. A methane storage comprising the metal-organic frameworkcomposite according to claim
 1. 9. A dye-captured metal-organicframework composite comprising (i) the metal-organic framework compositeaccording to claim 1, and (ii) a dye captured in the nano metal-organicframeworks.
 10. A method for producing a metal-organic frameworkcomposite, comprising (b) subjecting a solution comprising a secondmetal precursor, a second organic ligand, a second organic solvent, andnano metal-organic frameworks to a hydrothermal reaction wherein themetal-organic framework composite comprises a host metal-organicframework and nano metal-organic frameworks embedded in the hostmetal-organic framework, the second metal precursor is selected from Cu,Fe, Cr, Zn, At, Mg, Ni, Eu, Gd, and Tb precursors, the second organicligand is selected from BDC, BTC, BTB, BBC, BTB, BHEHPI, TATB, TPBTM,BTP, BTEI, BTTI, TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN, ImDC,DPBPyDC, PPy, THBTS, ADB, and BPP34C10DA, the second organic solvent isselected from dimethylformamide, diethylformamide,N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, methanol,ethanol, water, and mixtures thereof the host metal-organic frameworkand the nano metal-organic frameworks being represented by Formulae 1and 2, respectively:M1_(x1)O_(z1)(L1G1)_(y1)   (1)M2_(x2)O_(z2)(L1G2)_(y2)   (2) wherein M1 and M2 are different from eachother and are each independently selected from Cu, Fe, Cr, Zn, Al, Mg,Ni, Eu, Gd, and Tb, L1G1 and L1G2 are different from each other and areeach independently selected from BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB,TPBTM, BTP, BTEI, BTTI, TTBI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN,ImDC DPBPyDC, PPy, THBTS, ADB, and BPP34C10DA, x1 is an integer from 1to 6, x2 is an integer from 1 to 6, z1 is an integer from 1 to 4, z2 isan integer from 1 to 4, y1 is an integer from 1 to 6, and y2 is aninteger from 1 to
 6. 11. The method according to claim 10, furthercomprising (a) mixing a first metal precursor, a first organic ligand,and a first organic solvent and reacting the mixture with stirring atroom temperature to prepare the nano metal-organic frameworks whereinthe first metal precursor is selected from Cu, Fe, Cr, Zn, AL Mg, Ni,Eu, Gd, and Tb, the first organic ligand is selected from BDC, BTC, BTB,BBC, BTE, BHEHPI, TATB, TPBTM, BTP, BTEI, BTTI, TTEI, BTETCA, BNETPI,BHEI DOT, ATC, DCDPBN, ImDC, DPBPyDC, PPy, THBTS, ADB, and BPP34C10DA,and the first organic solvent is selected from dimethylformamide,diethylformamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide,dimethylacetamide, methanol, ethanol, water, and mixtures thereof. 12.The method according to claim 10, further comprising activating the nanometal-organic frameworks and the host metal-organic framework in ethanolor chloroform as a solvent for 30 to 40 hours, followed by drying undervacuum at 100 to 120° C.
 13. The method according to claim 10, whereinthe first metal precursor is a Cu precursor, the first organic ligand isBTC, the second metal precursor is a Zn precursor, the second organicligand is BDC, the first organic solvent is a mixture ofdimethylformamide, methanol, and water in a volume ratio of0.7-1:0.7-1:0.7-1, and the second organic solvent is diethylformamide.14. The method according to claim 13, wherein the Cu precursor and theBTC are in a weight ratio of 2.0-2.3:1.1-1.5.
 15. The method accordingto claim 13, wherein the Zn precursor and the BDC are in a weight ratioof 17-18:3.5-4.0.
 16. The method according to claim 10, wherein, thehydrothermal reaction is carried out at 110 to 130° C. for to 9 hours.17. A method for producing a dye-captured metal-organic frameworkcomposite, comprising (A) allowing a dye to be captured In nanometal-organic frameworks and (B) subjecting a solution of thedye-captured nano metal-organic frameworks, a second metal precursor, asecond organic ligand, and a second organic solvent to a hydrothermalreaction wherein the second metal precursor is selected from Cu, Fe, Cr,Zn, Al, Mg, Ni, Bu, Gd, and Tb, the second organic ligand is selectedfrom BDC, BTC, BTB, BBC, BTE, BHEHPI, TATB, TPBTM, BTP, BTEI, BTTI,TTEI, BTETCA, BNETPI, BHEI, DOT, ATC, DCDPBN, ImDC, DPBPyDC, PPy, THBTS,ADB, and BPP34C10DA, and the second organic solvent is selected fromdimethylformamide, diethylformamide, N-methyl-2-pyrrolidone, dimethyl,sulfoxide, dimethylacetamide, methanol, ethanol, water, and mixturesthereof.